The official covers of two 3D graphics cards, the ATI 1GB Radeon HD 4890 and the Nvidia 896MB GeForce GTX 275, came off Thursday morning.

At $250 for the baseline cards (overclocked models will be available for each for $10 or so more), these cards establish a new midrange battleground, filling the gap between the $150 and $300 price points we covered earlier this year.

Each of these cards, respectively from Advanced Micro Devices and Nvidia, has a two-slot PCI Express design that requires two six-pin cable connections to your PC's internal power supply. They also support each vendor's respective multicard technology, Crossfire for ATI, and SLI for Nvidia.

The ATI 1GB Radeon HD 4890.
Advanced Micro Devices

The Radeon HD 4890 doesn't introduce much in the way of new features, though it has a clock speed bump over its Radeon HD 4870 cards released last year. The core clock has gone from 750MHz on the 4870 to 850MHz on the 4890, and the memory from 900MHz to 950MHz.

AMD's ATI made a few other tweaks to memory bandwidth and fill rates, but for the most part, the two cards are very similar. The Radeon HD 4890 is available now at various online retailers, and prices so far reflect ATI's suggested $249 baseline.

The Nvidia 896MB GeForce GTX 275.
Nvidia

Nvidia's new GeForce GTX 275 is slated to become available for purchase on April 14. And while we don't imagine that Nvidia could simply make a new 3D card appear overnight (nor do we necessarily know which vendor actually started taping out its new card first), we find it interesting that mere days after ATI called us for a briefing on the Radeon HD 4890, Nvidia got in touch regarding its own new product.

That timing, along with the delayed availability and the fact that Nvidia seemed to be waiting for ATI to reveal its pricing first, suggest that the GTX 275 may be a reactionary launch to take the wind out of its competition. That doesn't make it any less of a 3D card, but some vocal Nvidia opponents have speculated that the GTX 275 might not hit the market in large quantities when it arrives.

In any case, the GeForce GTX 275 is basically a clocked-down GTX 285. The core, memory, and shader clocks on the new chip are respectively about 3 percent, 5 percent, and 9 percent slower than those of the GTX 285, and you also get less memory bandwidth.

Nvidia has also introduced an ambient occlusion feature in the driver that will launch with the GTX 275. This is basically a way to force soft shadows onto games that don't already support it, at the cost of some performance. Expect all current Nvidia cards to support ambient occlusion with the new driver, ForceWare version 185.65, available soon.

No one found a runaway winner, and as usual with cards from this generation, each has an advantage, depending on the game you want to play, as well as the settings. A few site reviews tipped in favor of Nvidia. We would add that AMD's new card is the only one you can actually buy at the moment.